Conventionally, when stenosis or occlusion occurs in vessels, such as blood vessels, and when blood vessels are blocked by thrombi, angioplasties (e.g., PTA: Percutaneous Transluminal Angioplasty and PTCA: Percutaneous Transluminal Coronary Angioplasty) are commonly performed in order to dilate narrowed areas or reopen occluded areas of blood vessels so that blood flow in the peripheries of blood vessels is improved. Many angioplasties have been performed in many medical institutions. Furthermore, in recent years, stents have been used to maintain the dilated state of narrowed areas in many cases.
A balloon catheter for PTA or PTCA is used together with a guiding catheter and a guidewire mainly for the purpose of dilating a narrowed area or occluded area of a blood vessel. In an angioplasty using the balloon catheter, first, the guiding catheter is inserted into the femoral artery and advanced through the aorta, and the tip of the guiding catheter is positioned in the opening of the coronary artery. Then, the guidewire passing through the balloon catheter is advanced beyond the narrowed area or occluded area of the blood vessel. The balloon catheter is advanced over the guidewire, and the balloon is inflated while being positioned at the narrowed area or occluded area so that the narrowed area or occluded area is dilated. The balloon is then deflated and removed from the body. The application of the balloon catheter is not limited to treatment of narrowed areas or occluded areas of blood vessels, and the balloon catheter is also useful for many other medical applications, such as insertion into blood vessels and insertion into various body cavities and tubular tissue structures.
However, when occlusion is caused by thrombi in the blood vessel, if the occluded area is dilated by the balloon catheter, there may be a possibility that the thrombi are detached from the inner wall of the blood vessel to occlude peripheral vessels downstream. In the case of the narrowed area of the blood vessel in which the lesion contains many athero-plaques, there may be a possibility that dilation by the balloon catheter leads to scattering of the athero-plaques (atheromas) to occlude peripheral vessels. When peripheral vessels are blocked as described above, even if the occluded area or narrowed area is dilated, blood is prevented from flowing into the peripheries, resulting in slow-flow or no-reflow.
When such a situation arises, in the coronary artery or the like, it is general practice to wait and see if the blood flow is recovered, but a long recovery time is required. According to circumstances, a vasodilator, such as nitroglycerin, may be administered to recover the blood flow, or a thrombolytic agent, such as urokinase, may be locally administered to dissolve the obstruction. In either case, a long recovery time is still required. When peripheral vessels are heavily occluded to produce poor hemodynamics, an auxiliary procedure, such as intra-aortic balloon pumping (IABP), may be used.
Besides the thrombolytic therapy, a method has been attempted in which thrombi are mechanically fragmented and a negative pressure is simultaneously applied from the proximal end of the catheter to remove the thrombi from the body.
However, in order to fragment a thrombus at the catheter tip, it is of course necessary to efficiently transmit the mechanical power applied from the proximal end of the catheter to the tip of the catheter. Consequently, in order to enhance the transmission of power in the catheter shaft, the entire catheter shaft must be composed of a hard material, resulting in difficulty in advancing the catheter to the target site in the blood vessel. Furthermore, since a negative pressure must be applied from the proximal end of the catheter simultaneously with the application of mechanical power, a large-scale device is required, and thus this method has not become widely used.
On the other hand, the effect of a catheter having a simple structure in which thrombi are removed by aspiration from the body by the application of a negative pressure from the proximal end has been clinically confirmed. However, the cross-sectional area of the aspiration lumen for aspiration is not sufficiently secured, and only catheters having low aspiration capability are available. The reason for this is that the catheter is advanced over the guidewire to the target site in the blood vessel. Namely, since a guidewire lumen tracking the guidewire is provided in the aspiration lumen, it is not possible to secure a sufficient cross-sectional area of the aspiration lumen.
On the other hand, in a structure in which a guidewire lumen is provided outside an aspiration lumen, the outer diameter of the aspiration catheter inevitably increases. Consequently, the inner diameter of the guiding catheter used together increases, resulting in an enormous burden to the patient.
In addition, since any of the guidewire lumens described above usually has a length of about 30 cm from the tip of the aspiration catheter, the catheter shaft lacks flexibility, resulting in poor insertability into tortuous blood vessels.